Japanese patent publication No. 1989-58031 discloses a power tool having a parallel-shaft type speed change mechanism. The known parallel-shaft type speed change mechanism has first and second drive gears having different numbers of teeth and fixed on a drive shaft, and first and second driven gears having different numbers of teeth and mounted on a driven shaft parallel to the drive shaft such that the driven gears are movable in the longitudinal direction. The first and second driven gears to be engaged with the first and second drive gears can be shifted by sliding the first and second driven gears along the driven shaft so that the speed of a motor can be changed to two speeds, or high speed and low speed, and transmitted to the tool bit.
According to the above-mentioned known parallel-shaft type speed change mechanism, when the position of the driven gears with respect to the drive gears is changed for speed change, it is difficult to smoothly engage the drive gears with the driven gears. In this connection, further improvement is desired in smoothness of speed changing operation.